add registered events view, finished lector view, optimizations

...es/migrations/0023_alter_lecturelector_avatar_and_more.py

lectures/models.py

lectures/templates/lectures/view_lector.html

lectures/templates/lectures/view_lecture.html

lectures/templates/lectures/view_registered.html

lectures/urls.py

lectures/views.py

requirements/base.txt

shared/templates/shared/includes/base.html